Control slump and moisture in your product by measuring the raw materials
Five moisture meters for different applications
Moisture measurement is an inexact science. The reason for this is the measurement zone, which is an area of a few square inches. Compared with the area of a typical feed gate in a bin, with an area of 150 to 350 square inches, it is very small. Consequently, aggregates falling from one side of the bin or another, with different moisture values, can escape inclusion in the average as the material flows. Also, different moisture sensor types are best suited to different materials and environments, as detailed below.
You need to do three things to guarantee success:
- Hold density constant, since all sensors are density sensitive. You can accomplish this by installing it in a bin and angling the sensing faceplate to slow and compact the material as it flows past.
- Make the measurement within the flow region, above the feed gate in a bin; not in the side where material does not flow.
- Average the readings while the material is flowing. It should hold the average between batches.
You should install your moisture probe in a bin or hopper where the material is compacted. This gives reliable density and therefore the most accurate moisture measurement. Also, smaller granule size, compared with the measurement aperture, gives higher accuracy. See a discussion of the various types of sensor here. We offer three types of sensor for different environments:
AquaSense 2280D is the best choice for measuring the moisture of sand and granular materials. Examples are fine aggregates (up to 1/4″ or 6 mm) or similar products that can be compacted inside a bin or hopper. The material flows across the moisture sensor and it averages the result during the flow period. This gives a better average than you can get from oven-dry tests. It can also be used in a ‘ski’ fixture that rides on top of a thick bed of material on a conveyor belt. As a result, however, this gives reduced accuracy. AquaSense 2280D is in use daily in concrete plants, sand and aggregate dryers, frac sand dryers, coal, animal feed mills and many food materials.
AquaSense 2280D is the ONLY moisture sensor with a 10 year guarantee!
For use in mixers for concrete and similar applications, AquaMix 2270D uses the hardest known material after diamond, Silicon Nitride, for its faceplate. Due to this, a life of over 10 years is typical in moisture measurement of extreme aggregates such as granite used daily in mixing of concrete. You install the moisture sensor in the floor of a pan, ribbon or twin-shaft mixer. A fixture allows you to adjust for the wear of the liner plates. Both AquaSense 2280D and AquaMix 2270D use the same setup and calibration software. If you want to mix widely different blends of material (for example lightweight and regular block mixes), you can store up to 10 different sets of calibration values in the sensor. You can access these through the serial digital connection.
If you do not have a batch controller or it does not have mixer moisture software, AquaControl 1540 can control the addition of water, based on readings from the AquaMix 2270D sensor. It connects to the moisture probe, water valves and meter. The controller is based on the same combination of PLC and touch screen used in BatchTron models. Because of this, three different methods are available to measure and add the water, depending on the application:
- MicroMix, a simple, calibration-free method that does not require a water meter.
- Fast MicroMix, requires a water meter but improves speed because it predicts the amount of fast pre-water, then adds it.
- MasterMix, which requires a water meter plus accurate sensor calibration. As a result, it gives the ultimate speed and accuracy.
The nir moisture sensor uses near-infrared (nir) light to measure the surface moisture of sand, aggregates and other granular materials as they pass by on a belt or flow out of a hopper. Polarmoist, sold in North America by Polarmatic, can measure the surface moisture of large aggregates (greater than 3/8″ or 10 mm). Capacitance and microwave moisture meters show too much variation. Because this method measures the surface of the material, it is less density sensitive than AquaSense 2280D. For the same reason, it can only measure the surface of the material stream and not the center or the average of the stream. Scale-Tron does not manufacture this item. It is available for these special applications or where clients prefer the near-infrared (nir) sensing method.
For applications requiring the ultimate accuracy, or for aggregate sizes up to 1.25″ (32mm) the Sono-Vario tdr moisture sensor, sold in North America by Mesa Systems Co. is best. Using Time-Domain Reflectometry (tdr) at radar frequencies gives deep penetration of the material, less sensitivity to density and consequently a better average. Its measurement accuracy is 0.1% as a result. It is mounted on a plate under the gate, in the stream of material. Scale-Tron does not manufacture this item. It is available for applications that demand the highest moisture measurement accuracy.